This invention relates to the field of image projectors. More particularly, this invention relates to the field of image projectors in which a laser illuminated light modulator produces an array of pixels and in which the array of pixels is projected onto a display screen.
In recent years, light modulators have been developed using MEMS (micro-electro-mechanical systems) technology in which moveable elements are configurable to direct light. An example of such light modulators is a grating light valve (GLV) taught in U.S. Pat. No. 5,311,360 to Bloom et al., in which the GLV is configurable in a reflecting mode and a diffracting mode. The GLV taught by Bloom et al. is isometrically illustrated in FIG. 1. The GLV 10 includes moveable elongated elements 12 suspended over a substrate 14.
A first side view of the GLV 10 of the prior art is illustrated in FIG. 2A, which shows the GLV 10 in the reflecting mode. The moveable elongated elements 12 each include a first reflective coating 16. Interspersed between the moveable elongated elements 12 are second reflective coatings 18. In the reflecting mode, upper surfaces of the first and second reflective coatings, 16 and 18, are separated by a height difference of a half wavelength xcex/2 of incident light I. The incident light I reflecting from the second reflecting coatings 18 travels a full wavelength further than the incident light I reflecting form the first reflecting coatings 16. So the incident light I, reflecting from the first and second reflecting coatings, 16 and 18, constructively combines to form reflected light R. Thus, in the reflecting mode, the GLV 10 produces the reflected light R.
A second side view of the GLV 10 of the prior art is illustrated in FIG. 2B, which shows the GLV in the diffracting mode. To transition from the reflecting mode to the diffracting mode, an electrostatic potential between the moveable elongated elements 12 and the substrate 14 moves the moveable elongated elements 12 to contact the substrate 14. To maintain the diffracting mode, the electrostatic potential holds the moveable elongated elements 12 against the substrate 14. In the diffracting mode, the upper surfaces of the first and second reflective coatings, 16 and 18, are separated by a quarter wavelength xcex/4 of the incident light I. The incident light I reflecting from the second reflecting surfaces 18 travels a half wavelength further than the incident light I reflecting from the first reflective coatings 16. So the incident light I, reflecting from the first and second reflecting coatings, 16 and 18, destructively interferes to produce diffraction. The diffraction includes a plus one diffraction order D+1 and a minus one diffraction order Dxe2x88x921.
Thus, in the diffracting mode, the GLV 10 produces the plus one and minus one diffraction orders, D+1 and Dxe2x88x921.
A first alternative GLV of the prior art is illustrated in FIGS. 3A and 3B. The first alternative GLV 10A includes first elongated elements 22 interdigitated with second elongated elements 23. The first elongated elements 22 include third reflective coatings 26; the second elongated elements 23 include fourth reflective coating 28. In the reflecting mode, illustrated in FIG. 3A, the third and fourth reflective coatings, 26 and 28, are maintained at the same height to produce the reflected light R. In the diffracting mode, illustrated in FIG. 3B, the first and second reflected coatings, 26 and 28, are separated by the second height difference of the quarter wavelength xcex/4 of the incident light I to produce the diffraction including the plus one and minus one diffraction orders, D+1 and Dxe2x88x921.
A display system utilizing a GLV is taught in U.S. Pat. No. 5,982,553 to Bloom et al. The display system includes red, green, and blue lasers, a dichroic filter group, illumination optics, the GLV, Schlieren optics, projection optics, a scanning mirror, and display electronics, which project a color image onto a display screen. The red, green, and blue lasers, driven by the display electronics and coupled to the GLV (via the dichroic filter group and the illumination optics) sequentially illuminate the GLV with red, green, and blue illuminations. The GLV, driven by the display electronics, produces a linear array of pixels which changes with time in response to a signal from the display electronics, each pixel configured in the reflecting mode or the diffracting mode at a given instant in time. Thus, the GLV produces sequential linear arrays of red, green, and blue pixels with each of the red, green, and blue pixels in the reflecting mode or the diffracting mode.
The red, green, and blue pixels are then coupled to the Schlieren optics which blocks the reflecting mode and allows at least the plus one and minus one diffraction order, D+1 and Dxe2x88x921, to pass the Schlieren optics. Thus, after passing the Schlieren optics, the linear arrays of the red, green, and blue pixels have light pixels corresponding to the pixels at the GLV in the diffracting mode and dark pixels corresponding to pixels at the GLV in the reflecting mode. The projection optics (via the scanning mirror) project the linear arrays of the red, green, and blue pixels onto the display screen while the scanning mirror, driven by the display electronics, scans the linear arrays of the red, green, and blue pixels across the display screen. Thus, the display system produces a two dimensional color image on the display screen.
An alternative display system utilizing the GLV includes the red, green, and blue lasers; red, green, and blue illumination optics; first, second, and third GLVs; the dichroic filter group; the projection optics; the scanning mirror; and the display electronics. The red, green, and blue lasers, via the red, green, and blue illumination optics, illuminate the first, second, and third GLVs, respectively. The first, second, and third GLVs produce the linear arrays of the red, green, and blue pixels, respectively, in response to signals from the display electronics. The dichroic filter group directs the linear arrays of the red, green, and blue pixels to the Schlieren optics, which allows at least the plus one and minus one diffraction order, D+1 and Dxe2x88x921, to pass the Schlieren optics. The projection optics, via the scanning mirror, project the linear arrays of the red, green, and blue pixels onto the display screen while the scanning mirror, driven by the display electronics, scans the linear arrays of the red, green, and blue pixels across the display screen. Thus, the alternative display system produces the two dimensional color image on the display screen.
Examples of applications for a GLV based display system include a home entertainment system, a boardroom application, and a cinema application among others. In the home entertainment system or the boardroom application, the GLV based display system projects the two dimensional color image onto the display screen located on a wall. In the cinema application, the GLV based display system projects the two dimensional color image from a display booth onto a cinema screen.
In the home entertainment system, the boardroom application, and the cinema application, the red, green, and blue lasers are bulky and, thus, take up space. Further, the red, green, and blue lasers generate heat and, thus, require cooling by a cooling apparatus. Moreover, power supplies for the red, green, and blue lasers as well as the cooling apparatus generates noise and vibration. Additionally, precise coming and control are required between laser electronics and projection electronics in such systems.
It is theorized that as a cinema house transitions from a film based projector to the GLV based display system, the cinema house will want to maintain the film based projector in the projection booth while adding the GLV based display system. Thus, in the cinema application the problem of space is an exceptionally difficult problem since there is generally not much extra room in the display booth to accommodate the GLV based display system while keeping the film based projector.
In addition, in the display system utilizing the GLV, configuring the illumination optics is geometrically difficult due to limited geometrical space for the illumination optics, the GLV, and the Schlieren optics. Very precise mechanical tolerances must be maintained between each of these parts. These problems are exacerbated in the alternative display system utilizing the GLV by a factor of three due to the red, green, and blue illumination optics illuminating the first, second, and third GLVs.
What is needed is a method of reducing the problems of space, heat, noise, and vibration in the home entertainment system, the boardroom application, and the cinema application. What is further needed is a method for adding a GLV based display system to a projection booth in a cinema application while keeping a film based projector in the projection booth.
What is needed is a method of reducing the problem of limited geometrical space for illumination optics illuminating a GLV in a single GLV based display system. What is further needed is a method of reducing the problem of limited geometrical space for illumination optics illuminating three GLVs in a three GLV based display system. Further, what is needed is a system that allows decoupling of the number of mechanical components which must be held within tight tolerances with respect to each other.
The present invention is an image projector which projects an image onto a display screen. The image projector includes a laser source unit, an optical fiber, and a projector head. The projector head includes a light modulator and an optical projection arrangement. The optical fiber couples a laser illumination to the light modulator of the projector head from the laser source unit. The light modulator modulates the laser illumination to produce an array of pixels. The optical projection arrangement projects the array of pixels onto the display screen to produce the image on the display screen.
Preferably, the image projector is a color image projector. In the color image projector, the laser source unit includes red, green, and blue lasers. The projector head of the color image projector preferably includes first, second, and third GLVs (grating light valves), and the optical projection arrangement. First, second, and third optical fibers couple the red, green and blue lasers of the laser source unit to the first, second, and third GLVs of the projector head. Preferably, the optical projection arrangement includes combining optics, separating optics, a projection lens, and a scanning mirror.
In operation the red, green, and blue lasers produce red, green, and blue laser illumination, which illuminate the first, second, and third GLVs. The first, second, and third GLVs modulate the red, green, and blue laser illuminations to produce red, green, and blue linear arrays of pixels. The red, green, and blue linear arrays of pixels include a diffracting mode and a reflecting mode. The separating optics allow at least plus one and minus one diffraction orders of the diffracting mode to pass the separating optics while blocking the reflecting mode. The projection lens, via the scanning mirror, projects the red, green, and blue linear arrays of pixels onto the display screen. The red, green, and blue linear arrays of pixels produce a color linear array of pixels on the display screen. The scanning mirror scans the red, green, and blue linear arrays of pixels across the display screen to produce a color image on the display screen.